Teachers are warning that secondary schools may close if they escalate their industrial action over pay cuts.
The ASTI is recommending its 17,000 members reject a revised version of the Haddington Road deal, prompting speculation that the Government may be forced to enact further cuts without agreement.
Teachers are already refusing to take part in meetings outside of school hours.
General Secretary of the ASTI Pat King says if there are further cuts, the union will be forced to act.
"If they do that, I've no doubt that the executive of the ASTI may meet, and they will direct teachers not to do it, and that could well close the school," he said.